Pellets, i.e. small round spherules, are known from the prior art as the basis for pharmaceutical formulations. Often, so-called “neutral” pellets consisting of maize starch and sucrose are used as the basis for pharmaceutical formulations in pellet form. It is also possible to use starter pellets which consist predominantly of an organic acid. A pellet formulation of this kind is disclosed for example in WO 03/074056. These formulations are compositions in which a layer of active substance which contains binder and optionally parting compounds is applied to a substantially spherical core material which consists of or contains the pharmaceutically acceptable organic acid, so as to enclose the core material. The core layer and the active substance layer are separated from one another by a so-called insulating layer. The structure of an active substance formulation of this kind is shown schematically in FIG. 1 of WO 03/074056.
The production of acid starter pellets of this kind with the required substantially spherical geometry has, however, proved unexpectedly difficult. In particular, there is always the possibility of excessive deviations from the desired spherical symmetry, for example with clumps formed by a larger sphere with smaller clumps adhering to the outside, forming so-called satellites. In pellet formulations in which the starter pellet is surrounded by an acid-sensitive active substance layer, these satellites may break off after the application of the insulating layer and thus give rise to defects in the insulation. This in turn has a detrimental effect on the storage stability of the active substance pellets.
The problem of the present invention is to provide so-called starter pellets which have a uniform, sphere-like geometry. In addition, they should have only a small number of potential defects in the insulation caused by satellites. It is particularly important to achieve as perfectly spherical a shape as possible and a low surface roughness for acid-sensitive active substances, where defects in the insulation caused by broken off satellites or by an excessively rough surface on over-sized particles of tartaric acid powder can lead to a significantly impaired storage stability and hence shelf life of the finished product. For this reason, with acid-sensitive active substances, it is also essential to apply the insulating layer as such with high reproducibility and a consistently high quality.